This revised Mentored Career Development Award application (K01) revolves around pseudoxanthoma elasticum (PXE), a Mendelian autosomal recessive disorder characterized by ectopic mineralization of connective tissues in a variety of organs, including the skin, eyes, and the cardiovascular system, with considerable morbidity and mortality. PXE results from mutations in the ABCC6 gene which encodes a putative transmembrane transporter protein, ABCC6, which is expressed primarily in the liver, to a lesser extent in kidneys, and at very low levels, if at all, in tissues affected by PXE. Adding to the complexity of this disorder are the observations that there is considerable inter- and intra-familil heterogeneity. Genetic factors, environmental, and life style variables also modulate the progression and eventual outcome of the disease. This application will expand upon baseline skills of the applicant, Dr. Qiaoli Li, to address the overall goal of identifying and characterizig the major and minor modifier genes of ectopic cutaneous mineralization, a predominant feature of PXE, using mouse genetic approaches. Crossing the severely affected KK/HIJ mice with unaffected C57BL/6J mice which are wild type for the Abcc6 allelic mutation, and crossing the severely affected KK/HIJ mice with unaffected DBA/2J mice with the same Abcc6 allelic mutation as KK/HIJ mice, allows examination of their N2 progeny for Quantitative Trait Locus (QTL) analysis to identify modifier genes that potentially modifies the cutaneous mineralization phenotype. Functional in vivo characterization of the candidate genes will prove their importance in ectopic mineralization process. It is expected that the results of this study will provide novel insights into the molecular pathways leading to phenotypic variability in PXE, with relevance to common disorders involving ectopic mineralization. Understanding such pathways is expected to provide opportunities for the development of novel pharmacologic approaches to ameliorate, and perhaps cure, these currently intractable conditions. Having both Drs. Jouni Uitto and John P. Sundberg on the mentoring team provides Dr. Li with an outstanding opportunity to take advantage of their expertise, learn about their diverse skill sets, and to utilze resources they have accumulated. These provide resources to immediately utilize for these studies which will support the applicant's progress into becoming an independent researcher.